U.S. patent number 6,687,598 [Application Number 10/107,490] was granted by the patent office on 2004-02-03 for method and system for controlling an engine with enhanced torque control.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. Invention is credited to Takeshi Ishino, Hiroyuki Itoyama, Hiroshi Iwano, Kenji Oota, Kensuke Osamura.
United States Patent |
6,687,598 |
Oota , et al. |
February 3, 2004 |
Method and system for controlling an engine with enhanced torque
control
Abstract
A method for controlling an engine comprises establishing a
torque correction coefficient (KA) to compensate for reducing
effect of available engine torque in operating range of different
excess air ratios (.lambda.) that are lower than a predetermined
value (unity=1). An initial base desired in-cylinder air mass
(tQacb) is determined based on a requested engine torque (tTe). A
desired excess air ratio (t.lambda.) is determined. The initial
base desired in-cylinder air mass (tQacb) is adjusted with at least
the desired excess air ratio (t.lambda.) and the correction
coefficient (KA) to generate a desired in-cylinder air mass (tQac).
A desired injected fuel mass (tQf) is controlled based on the
desired in-cylinder air mass (tQac) to deliver the requested engine
torque (tTe) with the desired excess air ratio (t.lambda.) held
accomplished.
Inventors: |
Oota; Kenji (Kanagawa,
JP), Iwano; Hiroshi (Kanagawa, JP),
Itoyama; Hiroyuki (Yokohama, JP), Ishino; Takeshi
(Chiba, JP), Osamura; Kensuke (Kanagawa,
JP) |
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
26612869 |
Appl.
No.: |
10/107,490 |
Filed: |
March 28, 2002 |
Foreign Application Priority Data
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|
|
|
|
Mar 30, 2001 [JP] |
|
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2001-101696 |
Nov 28, 2001 [JP] |
|
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2001-362935 |
|
Current U.S.
Class: |
701/104; 123/492;
123/568.21; 701/108 |
Current CPC
Class: |
F02D
35/0023 (20130101); F02D 41/005 (20130101); F02D
41/1497 (20130101); F02D 41/0002 (20130101); F02D
41/263 (20130101); F02D 41/1458 (20130101); F02D
2200/0614 (20130101); F02D 2200/1004 (20130101); Y02T
10/42 (20130101); Y02T 10/40 (20130101); F02D
2250/18 (20130101); F02D 41/0072 (20130101); F02D
2200/0402 (20130101); Y02T 10/47 (20130101) |
Current International
Class: |
F02D
35/00 (20060101); F02D 41/14 (20060101); F02D
41/00 (20060101); F02D 41/26 (20060101); F02D
033/02 (); F02D 035/00 (); F02D 041/14 (); F02D
041/26 (); F02M 025/07 () |
Field of
Search: |
;123/399,672,679,689,299,300,304,305,478,480,486,492,493,350,694,192.1
;701/101,102,103,104,105,108,109,115
;60/274,276,285,286,295,297,301,602,605.2 ;73/116,117.3,118.1,118.2
;700/44 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
408326595 |
|
Dec 1996 |
|
JP |
|
4083338318 |
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Dec 1996 |
|
JP |
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409014016 |
|
Jan 1997 |
|
JP |
|
11-294145 |
|
Oct 1999 |
|
JP |
|
Primary Examiner: Wolfe; Willis R.
Attorney, Agent or Firm: Foley & Lardner
Claims
What is claimed is:
1. A method for controlling an engine, the method comprising:
establishing a torque correction coefficient to compensate for
reducing effect of available engine torque in operating range of
different excess air ratios that are lower than a predetermined
value; determining an initial base desired in-cylinder air mass
based on a requested engine torque; determining a desired excess
air ratio; adjusting said initial base desired in-cylinder air mass
with at least said desired excess air ratio and said torque
correction coefficient to generate a desired in-cylinder air mass;
and determining a desired injected fuel mass based on said desired
in-cylinder air mass for fuel injection to deliver said requested
engine torque with said desired excess air ratio held
accomplished.
2. The method as claimed in claim 1, wherein said determining an
initial base desired in-cylinder air mass comprises determining
said requested engine torque based on a driver demand and an engine
speed.
3. The method as claimed in claim 2, wherein said determining an
initial base desired in-cylinder air mass comprises determining an
initial base desired in-cylinder air mass based on said requested
engine torque and the engine speed; and wherein said determining a
desired excess air ratio comprises determining a desired excess air
ratio based on said requested engine torque and the engine
speed.
4. The method as claimed in claim 1, further comprising determining
a desired EGR ratio; and wherein said adjusting said initial base
desired in-cylinder air mass with at least said torque correction
coefficient to generate a desired in-cylinder air mass comprises
adjusting said initial base desired in-cylinder air mass with said
torque correction coefficient and said desired EGR to generate said
desired in-cylinder air mass.
5. The method as claimed in claim 4, wherein said establishing a
torque correction coefficient comprises determining said torque
correction coefficient based on said desired excess air ratio.
6. The method as claimed in claim 4, wherein said establishing a
torque correction coefficient comprises determining said torque
correction coefficient based on an actual excess air ratio.
7. The method as claimed in claim 4, wherein said establishing a
torque correction coefficient comprises estimating an actual excess
air ratio based on an actual oxygen mass of EGR gas and an actual
airflow mass, and determining a torque correction coefficient based
on said estimated actual excess air ratio.
8. The method as claimed in claim 4, wherein said establishing a
torque correction coefficient comprises estimating an actual excess
air ratio based on a first delay gain that has been set accounting
for changes in said desired excess air ratio due to varying of
oxygen content of said airflow mass and a second delay gain that
has been set accounting for changes in said desired excess air
ratio due to varying of actual oxygen content of EGR gas, and
determining said torque correction coefficient based on said
estimated actual excess air ratio.
9. A computer readable storage media having stored data
representing instructions to control an engine, the computer
readable storage media comprising: instructions for establishing a
torque correction coefficient to compensate for reducing effect of
available engine torque in operating range of different excess air
ratios lower than a predetermined value; instructions for
determining an initial base desired in-cylinder air mass based on a
requested engine torque; instructions for determining a desired
excess air ratio; instructions for adjusting said initial base
desired in-cylinder air mass with at least said desired excess air
ratio and said torque correction coefficient to generate a desired
in-cylinder air mass; and instructions for determining a desired
injected fuel mass based on said desired in-cylinder air mass for
fuel injection to deliver said requested engine torque with said
desired excess air ratio held accomplished.
10. The computer readable storage media as claimed in claim 9,
wherein the instructions for determining an initial base desired
in-cylinder air mass based on a requested engine torque comprises:
instructions for determining said requested engine torque based on
an accelerator position and an engine speed.
11. The computer readable storage media as claimed in claim 10,
wherein the instructions for adjusting said initial base desired
in-cylinder air mass with at least said desired excess air ratio
and said torque correction coefficient comprises: instructions for
determining a EGR correction coefficient; and instructions for
adjusting said initial base desired in-cylinder air mass with said
EGR correction coefficient.
12. The computer readable storage media as claimed in claim 11,
wherein the instructions for determining a desired injected fuel
mass based on said desired in-cylinder air mass comprises:
instructions for determining said desired injected fuel mass based
on said desired in-cylinder air mass; and instructions for
delivering said desired injected fuel mass.
13. The computer readable storage media as claimed in claim 12,
wherein the instructions for establishing a torque correction
coefficient comprises: instructions for determining said torque
correction coefficient based on said desired excess air ratio.
14. The computer readable storage media as claimed in claim 12,
wherein the instructions for establishing a torque correction
coefficient comprises: instructions for detecting an actual excess
ratio; and instructions for determining said torque correction
coefficient based on said detected actual excess ratio.
15. The computer readable storage media as claimed in claim 12,
wherein the instructions for establishing a torque correction
coefficient comprises: instructions for estimating an actual excess
air ratio; and instructions for determining said torque correction
coefficient based on said estimated actual excess air ratio.
16. The computer readable storage media as claimed in claim 15,
wherein the instructions for estimating an actual excess air ratio
comprises: instructions for determining an intermediate desired
excess air ratio based on said requested engine torque and the
engine speed; instructions for establishing a quick delay gain
accounting for varying of fresh charge due to consumption of air by
the engine immediately after an engine throttle has been closed;
instructions for establishing a slow delay gain accounting for
varying of residual oxygen within EGR gas; instructions for
establishing an engine speed dependent correction coefficient based
on the engine speed; instructions for establishing an excess air
ratio dependent correction coefficient based on said intermediate
desired excess air ratio; instructions for correcting said quick
delay gain with said engine speed dependent correction coefficient
and said excess air ratio dependent correction coefficient to
generate a final quick delay gain; instructions for correcting said
slow delay gain with said engine speed dependent correction
coefficient and said excess air ratio dependent correction
coefficient to generate a final slow delay gain; instructions for
updating said intermediate desired excess air ratio using said
final quick delay gain to generate an intermediate desired excess
air ratio; and instructions for updating said intermediate desired
excess air ratio using said final slow delay gain to generate said
actual excess air ratio.
17. A system for controlling an engine, comprising: a plurality of
sensors for sensing a plurality of operating parameters of the
engine; and an ECU having control logic operative to establish a
torque correction coefficient to compensate for reducing effect of
available engine torque in operating range of different excess air
ratios that are lower than a predetermined value; to determine an
initial base desired in-cylinder air mass based on a requested
engine torque; to determine a desired excess air ratio; to adjust
said initial base desired in-cylinder air mass with at least said
desired excess air ratio and said torque correction coefficient to
generate a desired in-cylinder air mass; and to determine a desired
injected fuel mass based on said desired in-cylinder air mass for
fuel injection to deliver said requested engine torque with said
desired excess air ratio held accomplished.
18. A system for controlling an engine, comprising: means for
establishing a torque correction coefficient to compensate for
reducing effect of available engine torque in operating range of
different excess air ratios that are lower than a predetermined
value; means for determining an initial base desired in-cylinder
air mass based on a requested engine torque; means for determining
a desired excess air ratio; means for adjusting said initial base
desired in-cylinder air mass with at least said desired excess air
ratio and said torque correction coefficient to generate a desired
in-cylinder air mass; and means for determining a desired injected
fuel mass based on said desired in-cylinder air mass for fuel
injection to deliver said requested engine torque with said desired
excess air ratio held accomplished.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and system for
controlling an engine.
2. Description of the Background Art
Modern automotive engines have a controller and a combustion
chamber. The controller causes the combustion chamber to operate
alternately on a lean air/fuel mixture (oxygen excess) and a rich
air/fuel mixture (oxygen deficiency). The exhaust gases resulting
from combustion are supplied to a catalytic converter, which is
provided, inter alia, for reducing the nitrogen oxides.
Internal combustion engines of this kind are disclosed in U.S. Pat.
No. 5,437,153 issued Aug. 1, 1995 to Takeshima et al., and U.S.
Pat. No. 6,289,672 B1 issued Sep. 18, 2001 to Katoh et al.
Researches have used various names to refer to a catalytic
converter of the above-mentioned kind. For example, Takeshima et
al. called it "a NOx absorbent or trap." Katoh et al. called it "a
NOx occluding and reducing catalyst." In the following description,
the term "a NOx trap" is herein used to mean a catalytic converter
of the above kind.
A NOx trap utilizes alkali metal or alkaline earth metal in
combination with platinum in order to store or occlude the nitrogen
oxides when there is oxygen excess. When there is oxygen
deficiency, the NOx trap releases the trapped nitrogen oxides.
Under this operating condition called "purge mode", the oxygen is
withdrawn from the absorbed nitrogen oxides, and the hydrocarbons
(HC) and the carbon monoxides (CO) generated by the combustion are
all oxidized with this oxygen.
The NOx trap can, however, only absorbs a limited mass of nitrogen
oxides. As a result, the NOx trap must be purged after a certain
loading time in which it traps the nitrogen oxides. During the
purging or "NOx purge cycle," the NOx trap releases the nitrogen
oxides so that it can be charged anew. If the NOx trap is purged
too late, it is "filled" and can no longer absorb the nitrogen
oxides, allowing them to escape into the environment. If the NOx
trap is purged too long, it is "empty" and can no longer supply
nitrogen oxides as a source of oxygen for oxidizing the
hydrocarbons and carbon monoxides, allowing them to escape into the
environment.
The charging and purging of the NOx trap must therefore be
controlled. This is achieved by means of the oxygen inflow. During
oxygen excess, the catalytic converter is charged with nitrogen
oxides. During oxygen deficiency, the NOx trap is purged and
releases nitrogen oxides. In the above-mentioned Takeshima et al.,
the controller changes over from the oxygen excess to the oxygen
deficiency when estimate, in mass or amount, of the absorbed
nitrogen oxides exceeds a threshold.
In Takeshima et al., the controller causes an increase in fuel
injection time to make air/fuel mixture in the combustion chamber
rich when the oxygen deficiency is requested. Takeshima et al. also
discloses application to Diesel engine wherein the controller
causes an injector to feed reducing agent, such as, gasoline, into
the exhaust pipe before the catalytic converter when the oxygen
deficiency is requested.
In the above-mentioned Katoh et al., the controller causes a
secondary fuel injection in the expansion or exhaust stroke to
provide the oxygen deficiency when the engine operates on varying
of air/fuel ratios falling in a region of moderate lean air/fuel
mixtures with air/fuel ratios less than 20.
JP-A 11-294145 discloses an internal combustion engine equipped
with an injector for feeding reducing agent into the exhaust pipe
and an exhaust throttle upstream of the injector for restricting
flow of exhaust gas to minimize consumption of reducing agent. In
JP-A 11-294145, a controller, in response to request for the oxygen
deficiency, causes restriction of exhaust gas flow as well as
injection of reducing agent into the exhaust pipe for a catalyst to
release nitrogen oxides. To suppress a drop in available engine
torque due to pumping loss caused by the restriction of exhaust
gases, the controller causes an alteration of at least one engine
operating parameter to increase engine torque.
In the prior art, the secondary injection is carried out in
response to the oxygen deficiency request. Utilizing the secondary
injection causes an increase in fuel consumption. Besides, the fuel
used for the secondary injection does not contribute to combustion,
resulting in waste of energy. In the above-mentioned JP-A
11-294145, in order to compensate for reducing effect of available
engine torque due to pumping loss caused by restriction of exhaust
gas flow, the controller causes an increase in fuel to be
combusted. The amount of such increase in fuel is so determined as
to compensate for the reduction in available engine torque only
without any concern on possible alteration in composition of
exhaust gases resulting from the combustion of increased fuel with
the decreased excess air ratio (.lambda.). Although this control
strategy has utilized alteration of engine operating parameter to
compensate for the reducing effect of available engine torque, the
prior art fails to teach the enhanced torque control of the present
invention.
In the prior art, the air/fuel mixture is altered in response to
oxygen deficiency request. In the before-mentioned Takeshima et
al., engine operation on rich air/fuel mixture is accomplished in
response to the oxygen deficiency request. Under this operating
condition, the excess air ratio is or less than unity (.lambda.=1
or .lambda.<1). This control strategy fails to account for
alteration of available engine torque due to such change in
air/fuel mixture. Apparently, such alternation of available engine
torque is regarded as a problem in the before-mentioned Katoh et
al. To solve this problem, Katoh et al. teach changing over from
the oxygen excess to the oxygen deficiency when the alternation of
available engine torque is not noticeable to the operator.
Accordingly, the prior art has not yet to teach the enhanced torque
control of the present invention.
There is, therefore, a need to develop a control strategy for
controlling an engine utilizing enhanced engine torque control
operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and
system for controlling an engine through enhanced management of
various control parameters.
In carrying out the above object and other objects and features of
the present invention, there is provided a method for controlling
an engine. The method comprises establishing a correction
coefficient to compensate for reducing effect of available engine
torque in operating range of different excess air ratios that are
lower than a predetermined value. The method also comprises
determining an initial base desired in-cylinder air mass based on a
requested engine torque, and determining a desired excess air
ratio. The initial base desired in-cylinder air mass is adjusted
with at least the desired excess air ratio and the torque
correction coefficient to generate a desired in-cylinder air mass.
The method also comprises determining a desired injected fuel mass
based on the desired in-cylinder air mass for fuel injection to
deliver the requested engine torque with the desired excess air
ratio held accomplished.
A system is also provided for carrying out the method.
BRIEF DESCRIPTION OF THE DRAWINGS
Further objects and advantages of the invention will be apparent
from reading of the following description in conjunction with the
accompanying drawings.
FIG. 1 is a schematic block diagram of an internal combustion
engine and an electronic engine controller in accordance with one
embodiment of the present invention.
FIG. 2 is a simplified flowchart of a requested engine torque (tTe)
determination routine.
FIG. 3 is a curve illustrating data used to determine flow cross
sectional area (AAPO) versus driver demand (APO) in the form of
accelerator pedal position.
FIG. 4 is a curve illustrating data used to determine airflow ratio
(QH0) versus ratio (ADNV) that is a function of flow cross
sectional area (AAPO).
FIG. 5 is a set of curves illustrating data used to determine
requested engine torque (tTe) versus engine speed (Ne) and airflow
ratio (QH0).
FIG. 6 is a simplified flowchart of a desired exhaust gas
recirculation (EGR) rate (tEGR) determination routine.
FIG. 7 is a set of curves illustrating data used to determine
initial base desired EGR rate (tEGRb) versus engine speed (Ne) and
requested engine torque (tTe).
FIG. 8 is a curve illustrating data used to determine correction
coefficient (Kegr_tw) versus engine coolant temperature (Tw).
FIG. 9 is a simplified flowchart of a desired excess air ratio
(t.lambda.) determination routine.
FIG. 10 is a set of curves illustrating data used to determine
initial base desired excess air ratio (t.lambda.b) versus engine
speed (Ne) and requested engine (tTe).
FIG. 11 is a curve illustrating data used to determine correction
coefficient (HOS_t .lambda.) versus engine coolant temperature
(Tw).
FIG. 12 is a simplified flowchart of a desired equivalence ratio
(tFBYA) determination routine.
FIG. 13 is a simplified flowchart of a routine including
determination of initial base desired in-cylinder air mass (tQacb),
establishment of torque correction coefficient (KA), and adjustment
of initial base desired in-cylinder air mass (tQacb) to generate
desired in-cylinder air mass (tQac).
FIG. 14 is a set of curves illustrating data used to determine
initial base desired in-cylinder air mass (tQacb) versus engine
speed (Ne) and requested engine torque (tTe).
FIG. 15 is a curve illustrating data used to establish torque
correction coefficient (KA) versus excess air ratio (.lambda.).
FIG. 16 is a simplified flowchart of a desired injected fuel mass
(tQf).
FIG. 17 is a simplified flowchart of a desired throttle position
(tTPO) computation routine.
FIG. 18 is a simplified flowchart of a desired EGR valve position
(tEGR) computation routine.
FIG. 19 is a simplified flowchart of an actual airflow (Qas0)
computation routine.
FIG. 20 is a curve used to determine airflow (Qas0_d) versus
airflow signal.
FIG. 21 is a simplified flowchart of an in-collector air mass
(Qacn) computation routine.
FIG. 22 is a simplified flowchart of an actual in-cylinder air mass
(rQac) computation routine.
FIG. 23 is a simplified flowchart of an actual in-cylinder EGR mass
(rQec) computation routine.
FIG. 24 is a simplified routine of an actual in-cylinder EGR ratio
(rEGR) computation routine.
FIG. 25 is a simplified routine of a collector volume delay (CVD)
time constant (Kkin) computation routine.
FIG. 26 is a set of curves illustrating data used to determine a
base volume efficiency (Kinb) versus engine speed (Ne) and desired
injected fuel mass (tQf).
FIG. 27 is a simplified flowchart of an estimated actual excess air
ratio (r.lambda.) computation routine.
FIG. 28 is a simplified flow chart of an estimated actual excess
air ratio (r.lambda.) computation routine.
FIG. 29 is a curve illustrating data used to determine an engine
speed dependent correction coefficient (HOS_Ne) versus engine speed
(Ne).
FIG. 30 is a curve illustrating data used to determined an excess
air ratio dependent correction coefficient (HOS_A) versus
intermediate desired excess air ratio (t.lambda.0).
FIG. 31 is a block diagram illustrating a method of the present
invention for controlling an engine.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the accompanying drawings, and initially to FIG.
1, a schematic block diagram of an internal combustion engine and
an electronic engine controller in accordance with one embodiment
of the present invention is illustrated. The internal combustion
engine 10 includes a plurality of combustion chambers, or
cylinders, one of which is shown in FIG. 1. The electronic engine
controller (EEC) 12 controls the engine 10.
The EEC 12 is preferably a microcomputer-based controller.
Controller 12 includes a microprocessor (MPU) 14 in communication
with input and output (I/O) ports 16, and computer readable storage
media 18 via a data control bus 20. Computer readable storage media
18 may include various types of volatile and nonvolatile memory
such as read only memory (ROM) 22, random access memory (RAM) 24
and keep-alive memory (KAM) 26. These "functional" descriptions of
the various types of volatile and nonvolatile storage may be
implemented by any number of known physical devices including but
not limited to EPROMs, EEPROMs, PROMs, flash memory, and the like.
Computer readable storage media 18 include stored data representing
instructions executable by microprocessor 14 to implement the
method for controlling engine according to the present
invention.
The EEC 12 receives a plurality of signals from the engine 10 via
I/O ports 16. These signals include, but are not limited to, a
cylinder identification (CID) signal 28 from a cylinder
identification (CID) sensor 30, an engine coolant temperature (ECT)
signal 32 from an engine coolant temperature (ECT) sensor 34, an
accelerator pedal position (APP) signal 36 from an accelerator
pedal position (APP) sensor 38, and an airflow signal 40 from an
airflow sensor 42. APP sensor 38 provides APP signal 36, which is
an indication of the position of an accelerator pedal 44
manipulated by the driver. The driver manipulates accelerator pedal
44 to control the output of a powertrain, not shown, including
engine 10.
Controller 12 processes these signals received from engine 10 and
generates a fuel injector signal transmitted on signal line 46 to
fuel injector 48 to control the amount of fuel delivered by the
fuel injector 48. A pump 50 sends fuel from a fuel tank, not shown,
through a common rail 52 to a set of fuel injectors 48. Fuel
injectors 48 are positioned to inject fuel into their associated
combustion chambers in amounts as determined by controller 12. The
fuel tank contains liquid fuel, such as gasoline, methanol or a
combination of fuel types.
An exhaust system 54 transports exhaust gas produced from
combustion of an air/fuel mixture in the combustion chambers to a
NOx trap 56 composed of material of the type previously described.
NOx trap 56 is contained in a housing 58. Exhaust system 54
includes an exhaust manifold 60. An exhaust gas oxygen sensor (EGO)
sensor 62 may be provided, which detects or measures the oxygen
content of the exhaust gas produced by combustion within the
combustion chambers, and transmits an oxygen signal 64 to
controller 12. In the engine illustrated in FIG. 1, a turbine 66 of
a supercharger 68 is disposed in exhaust system 54 downstream of
exhaust manifold 60 and upstream of NOx trap 56.
Supercharger 68 includes a compressor 70 downstream of airflow
sensor 42, which is disposed downstream of an air cleaner 72 of an
intake system 74. Intake system 74 includes an intake pipe 76 and
an intake manifold 78. An intercooler 80 is disposed downstream of
compressor 80 to send conditioned intake air to intake manifold 78.
Intake manifold 78 includes a collector 82. A throttle valve of the
electromagnetically controlled type 84 is disposed upstream of
collector 82. Throttle 84 opens in response to a throttle command
signal 86. Intake valve 88 operates to open and close its
associated intake port to control entry of air into combustion
chamber. Intake valve 88 in combination with a swirl control valve
(SCV) 90 allows for two-stage manifold operation including a swirl
generation operation.
An exhaust gas recirculation (EGR) system 92 transports a portion
of exhaust gas from exhaust manifold 60 to collector 82 of intake
manifold 78. EGR system 92 includes a passage 94 having one end
connected to exhaust manifold 60 and opposite end connected to
collector 82. An EGR control valve 96 receives an EGR command
signal 98 to control flow of exhaust gas through passage 94.
Requested engine torque tTe determination routine 100 executed by
controller 12 is shown in the flowchart of FIG. 2. Controller 12
executes this routine 100 and each of the following routines at
regular intervals of 10 milliseconds.
At step 102, controller 12 reads APP signal 36 to determine a
driver demand APO, and reads CID signal 28 to determine an engine
speed Ne. At step 104, controller 12 determines an effective cross
sectional area AAPO versus driver demand APO using stored data
illustrated by a curve 106 in FIG. 3. Curve 106 shows one of
various examples of a pattern of variation of effective cross
sectional area AAPO against driver demand APO. The pattern of
variation may be set accounting for varying of performances with
different types of vehicles. According to another example,
effective cross sectional area AAPO increases at a gradual rate as
driver demand APO increases initially and at an increased rate as
driver demand APO increases further. Turning back to FIG. 2, at
step 108, controller 12 computes a ratio ADNV, which may be
expressed as:
where: VOL# is the displacement of an engine.
At step 110, controller 12 determines an airflow ratio QH0 versus
the ratio ADNV using stored data as illustrated by a curve 112 in
FIG. 4. Curve 112 illustrates how much effective cross sectional
area AAPO should increase if a need arises to accomplish an
increase in in-cylinder air mass from the stoichiometric air/fuel
ratio state. In FIG. 2, at step 114, controller 12 determines
requested engine torque tTe versus engine speed Ne and airflow
ratio QH0 using stored data illustrated by a set of curves 116,
118, 120, 122, 124 and 126 in FIG. 5. Each of these curves
represents an equal value of QH0 versus different engine speeds Ne
and requested engine torque tTe. The values represented by these
curves increase in the direction of an arrow 128.
Desired EGR ratio tEGR computation routine 130 executed by
controller 12 is shown in the flowchart of FIG. 6. At step 132,
controller 12 inputs engine speed Ne and requested engine torque
tTe, and reads ECT signal 32 to determine engine temperature Tw. At
step 134, controller 12 determines an initial base desired EGR
ratio tEGRb using stored data illustrated by a set of curves 136,
138 and 140 in FIG. 7. Each of these curves represents an equal
value of tERGb versus different engine speeds Ne and requested
engine torque tTe. The values represented by these curves increase
in the direction of an arrow 142. In FIG. 6, at step 144,
controller 12 determines an engine temperature dependent correction
coefficient Kegr_tw using stored data illustrated by a curve 146 in
FIG. 8. Curve 146 shows that correction coefficient Kegr_tw stays
at 1.0 when engine temperature Tw falls a narrow range extending in
the neighborhood of 80.degree. C., but it drops from 1.0 toward
zero as engine temperature Tw drops beyond the lower limit of the
range or increases beyond the upper limit of the range. In FIG. 6,
at step 148, controller 12 computes desired EGR ratio tEGR, which
may be expressed as:
Desired excess air ratio t.lambda. determination routine 150
executed by controller 12 is shown in the flowchart of FIG. 9. At
step 152, controller 12 inputs engine speed Ne and requested engine
torque tTe. At step 154, controller 12 determines an initial base
desired air excess ratio tAb versus engine speed Ne and requested
engine torque tTe using stored data illustrated by a set of curves
156, 158 and 160 in FIG. 10. Each of these curves represents an
equal value of tAb versus different engine speeds Ne and requested
engine torque tTe. The values represented by these curves increase
in the direction of an arrow 162. In FIG. 9, at step 164,
controller 12 determines an engine temperature dependent correction
coefficient HOS_t.lambda. versus engine temperature Tw using stored
data illustrated by a curve 166 in FIG. 11. Curve 166 shows that
correction coefficient HOS_t.lambda. stays at 1.0 when engine
temperature is not less than 80.degree. C., but it increases from
1.0 as engine temperature Tw drops below 80.degree. C. In FIG. 9,
at step 168, controller 12 computes a desired excess air ratio
t.lambda., which may be expressed as:
From the above description along with FIGS. 9 to 11, it is
appreciated that desired excess air ratio t.lambda. is equal to
initial base desired excess air ratio t.lambda.b when engine
temperature is not less than 80.degree. C. although the former
deviates from the latter when engine temperature Tw drops below
80.degree. C. As shown in FIG. 10, engine speed Ne and requested
engine torque tTe determine initial base desired excess air ratio
t.lambda.b, which, in turn, determines desired excess air ratio
t.lambda..
The excess air ratio .lambda. may be expressed as:
Desired equivalence ratio tFBYA computation routine 170 executed by
controller 12 is shown in the flowchart of FIG. 12. At step 172,
controller 12 inputs desired EGR ratio tEGR and desired excess air
ratio t.lambda.. At step 174, controller 11 computes desired
equivalence ratio tFBYA, which may be expressed as:
Desired in-cylinder air mass tQac computation routine 180 executed
by controller 12 is shown in the flowchart of FIG. 13. The routine
180 includes determination of an initial base desired in-cylinder
air mass tQacb, establishment of a torque correction coefficient
KA, and adjustment of the initial base desired in-cylinder air mass
tQacb to generate a desired in-cylinder air mass tQac.
At step 182, controller 12 inputs engine speed Ne, requested engine
torque tTe, desired EGR ratio tEGR and desired excess air ratio
t.lambda.. At step 184, controller 12 determines initial base
desired in-cylinder air mass tQacb versus engine speed Ne and
requested engine torque tTe using stored data illustrated by a set
of curves 186, 188 and 190 in FIG. 14. Each of these curves
represents an equal value of tQacb versus different engine speeds
Ne and requested engine torque tTe. The values represented by these
curves increase in the direction of an arrow 192. In FIG. 13, at
step 194, controller 12 computes a correction coefficient kQacegr,
which may be expressed as:
At step 196, controller 12 establishes a torque correction
coefficient KA to compensate for reducing effect of available
engine torque in operating range of different excess air ratios
.lambda. that are lower than a predetermined value of 1. In one
embodiment, controller 12 determines torque correction coefficient
KA versus desired excess air ratio t.lambda. using stored data
illustrated by a curve 198 in FIG. 15. In this case, controller 12
retrieves curve 198 using desired excess air ratio t.lambda. as
excess air ratio .lambda.. In other embodiments, controller 12
determines torque correction coefficient KA versus actual excess
air ratio r.lambda. using stored data illustrated by curve 198 in
FIG. 15. In such case, controller 12 retrieves curve 198, using
actual excess air ratio r.lambda.. As will be later described along
with the flowchart of FIG. 27 or 28, controller 12 computes
estimated actual excess air ratio r.lambda. for establishing torque
correction coefficient KA. Turning back to FIG. 13, at step 200,
controller 12 adjusts initial base desired in-cylinder air mass
tQacb with at least desired excess air ratio t.lambda. and torque
correction coefficient KA to generate a desired in-cylinder air
mass tQac. In the embodiment, controller 12 computes desired
in-cylinder air mass tQac, which may be expressed as:
With reference to FIG. 15, curve 198 shows that torque correction
coefficient KA is held at 1.0 when excess air ratio .lambda. is
equal to 1 or greater than 1. However, when excess air ratio
.lambda. is set less than 1 to cause air/fuel mixture to make rich
to purge NOx from NOx trap 56, torque correction coefficient KA
takes a value greater than 1.
Desired injected fuel mass tQf determination routine 210 executed
by controller 12 is shown in the flowchart of FIG. 16. At step 212,
controller 12 inputs desired in-cylinder air mass tQac and desired
equivalence ratio tFBYA. At step 214, controller 12 determines a
desired injected fuel mass tQf, which may be expressed as:
where: BLAMB# is the stoichiometric air/fuel ratio.
Controller 12 generates fuel injector signal based on desired
injected fuel mass tQf so that fuel injectors 48 inject fuel to
achieve the desired injected fuel mass tQf in the associated
cylinders.
From the preceding description, it is now understood from equation
(5) that desired equivalence ratio tFBYA accounts for both the rate
of oxygen of desired EGR ratio tEGR and desired excess air ratio
t.lambda.. In the embodiment, as is clear from equation (8), this
desired equivalence ratio tFBYA is multiplied with desired
in-cylinder air mass tQac to determine desired injected fuel mass
tQf, making it possible to achieve desired EGR ratio tEGR and
desired excess air ratio t.lambda. even if they are subject to
great changes, respectively.
From the preceding description along the flowchart of FIG. 13, it
is now understood that desired in-cylinder air mass tQac results
from adjustment of initial desired in-cylinder air mass tQacb with
at least desired excess air ratio t.lambda. and torque correction
coefficient KA. In the embodiment, desired in-cylinder air mass
tQac also accounts for desired EGR ratio tEGR by using correction
coefficient kQacegr in adjusting initial base desired in-cylinder
air mass tQacb in determining desired in-cylinder air mass tQac. In
one embodiment, to achieve this desired in-cylinder air mass tQac,
controller 12 generates throttle command signal 86 to control
throttle 84. In another embodiment, to achieve desired in-cylinder
air mass tQac, controller 12 generates EGR command signal 98 to
control EGR control valve 96.
Desired throttle position tTPO computation routine 220 executed by
controller 12 is shown in the flowchart of FIG. 17. At step 222,
controller 12 computes an air mass error .DELTA.Qac, which may be
expressed as:
where: rQac is the actual in-cylinder air mass that may be
estimated by executing actual in-cylinder air mass computation
routine 260 shown in the flowchart of FIG. 22.
At step 224, controller 12 computes a desired throttle position
throttle tTPO, which may be expressed as:
The computation to give desired throttle position tTPO represents
the so-called proportional integral control (PI control). The gains
Kp and Ki may be fixed values, respectively, or may be altered
accounting for different operating conditions. In the embodiment,
the PI control has been employed. But, such PI control may combine
with the feedforward control.
Desired EGR valve position tEGRv computation routine 230 executed
by controller 12 is shown in the flowchart of FIG. 18. At step 232,
controller 12 computes an air mass error .DELTA.Qac, which may be
expressed by equation (9). At step 234, controller 12 computes a
desired EGR valve position tEGRv, which may be expressed as:
The computation to give desired EGR valve position tEGRv represents
the so-called proportional integral control (PI control). The gains
Kp2 and Ki2 may be fixed values, respectively, or may be altered
accounting for different operating conditions. In the embodiment,
the PI control has been employed. But, such PI control may combine
with the feedforward control.
Controller 12 executes desired EGR valve position tEGRv computation
routine 230 to alter actual in-cylinder air mass rQac. If it is
desired to cause an increase in actual in-cylinder air mass rQac,
controller 12 moves EGR control valve 96 in a closing direction to
decrease EGR gas portion of the cylinder charge. If it is desired
to cause a reduction in actual in-cylinder air mass rQac,
controller moves EGR control valve 96 in an opening direction to
increase EGR gas portion of the cylinder charge.
The PI gains, which include Kp, Ki, Kp2 and Ki2, are greater than 0
(zero).
To estimate actual in-cylinder air mass rQac, controller 12
executes routines shown in the flowcharts of FIGS. 19, 21 and
22.
Actual airflow Qas0 computation routine 240 executed by controller
12 is shown in the flowchart of FIG. 19. At step 242, controller 12
reads airflow signal 40. At step 244, controller 12 determines
detected airflow Qas0_d versus airflow signal 40 using stored data
illustrated by a curve 246 in FIG. 20. Curve 236 shows the
relationship between detected airflow Qas0_d and airflow signal 40
from airflow sensor 42. At step 248, controller 12 computes the
weighted average Qas0 of detected airflow Qas0_d.
In-collector air mass Qacn computation routine 250 executed by
controller 12 is shown in the flowchart of FIG. 21. At step 252,
controller 12 inputs engine speed Ne. At step 254, controller 12
computes air mass per one cylinder Qac0, which may be expressed
as:
At step 256, controller 12 processes Qac0 accounting for
transportation delay from airflow sensor 42 to collector 82 to
compute in-collector air mass Qacn, which may be expressed as:
Actual in-cylinder air mass rQac computation routine 260 executed
by controller 12 is shown in the flowchart of FIG. 22. At step 262,
controller 12 inputs in-collector air mass Qacn and an accumulation
coefficient Kkin, which is updated by execution of routine shown in
the flowchart of FIG. 25. At step 264, controller 12 processes Qacn
using Kkin to compute actual in-cylinder air mass rQac, which may
be expressed as:
To estimate actual in-cylinder EGR mass rQec, controller 12
executes routine shown in the flowchart of FIG. 23.
Actual in-cylinder EGR mass rQec computation routine 270 executed
by controller 12 is shown in FIG. 23. At step 272, controller 12
inputs actual in-cylinder air mass rQac, desired EGR ratio tEGR and
accumulation coefficient Kkin. At step 274, controller 12 computes
in-collector EGR mass Qec0, which may be expressed as:
At step 276, controller 2 computes actual in-cylinder EGR mass
rQec, which may be expressed as:
To estimate actual in-cylinder EGR ratio rEGR, controller 12
executes routine shown in the flowchart of FIG. 24.
Actual in-cylinder EGR ratio rEGR computation routine 280 executed
by controller 12 is shown in the flowchart of FIG. 24. At step 282,
controller 12 inputs actual in-cylinder air mass rQac and actual
in-cylinder EGR mass rQec. At step 284, controller 12 computes
actual in-cylinder EGR ratio rEGR, which may be expressed as:
The before-mentioned accumulation coefficient Kkin is updated by
execution of routine shown in the flowchart of FIG. 25.
Accumulation coefficient Kkin computation routine 290 executed by
controller 12 is shown in the flowchart of FIG. 25. At step 292,
controller 12 inputs engine speed Ne, desired injected fuel mass
tQf and actual EGR ratio rEGR. At step 294, controller 12
determines a base volume efficiency Kinb versus engine speed Ne and
desired injected fuel mass tQf using stored data illustrated by a
set of curves 296, 298 and 300 in FIG. 26. Each of these curves
represents an equal value of Kinb versus different engine speeds Ne
and desired injected fuel mass tTe. The values represented by these
curves increase in the direction of an arrow 302.
In FIG. 25, at step 304, controller 12 computes calibrated value
Kinc of base volume efficiency Kinb. Calibrated value Kinc may be
expressed as:
At step 306, controller 12 computes accumulation coefficient Kkin,
which may be expressed as:
With reference again to FIG. 15, torque correction coefficient KA
is given by retrieving curve 198 using desired excess air ratio
t.lambda. in the exemplary embodiment. In this case, a shift in
desired excess air ratio t.lambda. to a value less than 1 to purge
NOx from NOx trap 56 causes a step-like increase in actual injected
fuel mass rQf followed by a gradual increase in actual in-cylinder
air mass rQac. There occurs over enriched state until the desired
excess air ratio is achieved. If it is desired to trim unnecessary
consumption of fuel until desired excess air ratio t.lambda. is
achieved, actual excess air ratio r.lambda. is used instead of
desired excess air ratio t.lambda. in retrieving curve 198 in FIG.
15 to determine torque correction coefficient KA.
With reference to FIGS. 27-30, in the following description, two
examples of estimating actual excess air ratio r.lambda. will be
described.
In one exemplary embodiment, controller 12 estimates actual excess
air ratio r.lambda. by execution of estimated actual excess air
ratio r.lambda. routine 310 shown in the flow chart of FIG. 27.
In FIG. 27, at step 312, controller 12 computes EGR mass per one
cylinder Qecn, which may be expressed as:
At step 314, controller 12 computes actual in-cylinder EGR mass
rQec, which may be expressed as:
At step 316, controller 12 computes the rate of oxygen Ko.sub.2
remaining in EGR gas. Which may be expressed as:
At step 318, controller 12 computes a total in-cylinder air mass
Qaec, which may be expressed as:
At step 320, controller 12 computes estimated actual excess air
ratio r.lambda., which may be expressed as:
The estimated actual excess air ratio r.lambda. closely
approximates the actual variation of cylinder charge because it
accounts for oxygen content of new charge, oxygen content remaining
in EGR gas as well as delay and diffusion of EGR gas within intake
manifold. According to this exemplary embodiment, estimated actual
excess air ratio r.lambda. is used in step 196 of routine 180 shown
in the flowchart of FIG. 13.
In another exemplary embodiment, controller 12 estimates actual
excess air ratio r.lambda. by execution of estimated actual excess
air ratio r.lambda. computation routine 330 shown in the flowchart
of FIG. 28. At step 332, controller 12 inputs engine speed Ne and
requested engine torque tTe. At step 334, controller 12 determines
an initial base desired air excess ratio t.lambda.b versus engine
speed Ne and requested engine torque tTe using stored data
illustrated by a set of curves 156, 158 and 160 in FIG. 10. At step
336, controller 12 determines an engine temperature dependent
correction coefficient HOS_t.lambda. versus engine temperature Tw
using stored data illustrated by a curve 166 in FIG. 11. At step
338, controller 12 computes an intermediate desired excess air
ratio t.lambda.0, which may be expressed as:
At step 340, controller 12 determines an engine speed dependent
correction coefficient HOS_Ne versus engine speed Ne using stored
data illustrated by a curve 342 in FIG. 29. At step 344, controller
12 determines an excess air ratio dependent correction coefficient
HOS_.lambda. versus intermediate desired excess air ratio
t.lambda.0 using stored data illustrated by a curve 346 in FIG.
30.
At step 348, controller 12 corrects a quick delay gain GAIN 1 with
correction coefficients HOS_Ne and HOS_.lambda.. The manner of such
correction may be expressed as:
It is to be noted that the quick delay gain GAIN 1 is a relatively
quick component of a delay, which has been determined accounting
for quick varying of fresh charge due to consumption of air by the
engine immediately after engine throttle 84 has been closed.
At step 350, controller 12 corrects a slow delay gain GAIN 2 with
correction coefficients HOS_Ne and HOS_.lambda.. The manner of such
correction may be expressed as:
It is to be noted that the slow delay gain GAIN 2 is a relatively
slow component of a delay, which has been determined accounting for
slow varying of residual oxygen within EGR gas.
At step 352, controller 12 computes a second intermediate desired
excess air ratio t.lambda.1, which may be expressed as:
At step 354, controller 12 computes an estimated actual excess air
ratio r.lambda., which may be expressed as:
According to this exemplary embodiment, estimated actual excess air
ratio r.lambda. is used in step 196 of routine 180 shown in the
flowchart of FIG. 13.
In other exemplary embodiment, controller 12 determines actual
excess air ratio r.lambda. by reading oxygen signal 64 from an EGR
sensor 62 (see FIG. 1). In this case, controller 12 utilizes this
detected actual excess air ratio r.lambda. is used to retrieve
curve 198 in FIG. 15.
With reference to FIG. 31, a method of the present invention for
controlling an engine is generally indicated at 360. At block 362,
a torque correction coefficient KA is established to compensate for
reducing effect of available engine torque in operating range of
different excess air ratios .lambda. that are lower than a
predetermined value (see FIG. 15). At block 364, an initial base
desired in-cylinder air mass tQacb is determined based on a
requested engine torque tTe. At block 366, a desired excess air
ratio t.lambda. is determined. At block 368, an initial base
desired in-cylinder air mass tQacb is adjusted with at least the
desired excess air ratio t.lambda. and the torque correction
coefficient KA to generate a desired in-cylinder air mass tQac. At
block 370, a desired injected fuel mass tQf is determined based on
the desired in-cylinder air mass tQac for fuel injection to deliver
the requested engine torque tTe with the desired excess air ratio
t.lambda. held accomplished.
While the present invention has been particularly described, in
conjunction with exemplary embodiments, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art in light of the foregoing description. It
is therefore contemplated that the appended claims will embrace any
such alternatives, modifications and variations as falling within
the true scope and spirit of the present invention.
This application claims the priority of Japanese Patent
Applications No. P2001-101696, filed Mar. 30, 2001, and No.
P2001-362935, filed Nov. 28, 2001, the disclosure of each of which
is hereby incorporated by reference in its entirety.
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